1. Field of the Invention
This invention relates to an abrasive article having a sheet-like structure having a major surface with a plurality of abutting abrasive composites deployed thereon. This invention also relates to a process of making such an abrasive article, and a method of using such an abrasive article to provide an improved cut rate and surface finish.
2. Discussion of the Art
In general, abrasive articles comprise a plurality of abrasive particles bonded either together (e.g., a bonded abrasive or grinding wheel) or to a backing (e.g., a coated abrasive). These abrasive articles have been utilized to abrade and finish workpieces for well over a hundred years. One problem that has always plagued the abrasive industry is the generally inverse relationship associated between the cut rate (i.e., the amount of workpiece removed for a given time interval) and the surface finish that is imparted by the abrasive article on the workpiece surface. This explains why there exists a wide range of abrasive products from coarse grit (i.e., relatively large particle size of abrasive particles) to fine grit (i.e., relatively small particle size of abrasive particles). Typically, these different types of abrasive products are sequentially used in an abrading operation to achieve both the desired cut and surface finish.
What is desired by the industry is an abrasive article that gives a relatively high rate of cut, while still imparting a relatively fine surface finish on the workpiece being abraded.
One solution to this problem is disclosed in U.S. Pat. No. 5,152,917 (Pieper et al.). Pieper et al. teach a structured abrasive that is loading resistant and provides a consistency in the surface finish provided in the workpiece surface. The structured abrasive comprises abrasive composites that are bonded to a backing and that have a precise shape. Pieper et al. state a general premise that a higher areal density of abrasive composites tends to produce a lower unit pressure per composite during grinding, therby allowing a finer surface finish. However, Pieper et al. only exemplified a lineal spacing of abrasive composites of about 0.017 inches (0.007 cm), or an areal spacing of only about 536 composites/square centimeter. Pieper et al. indicate that an abrasive article with this spacing of pyramidal shaped composites was thought to satisfy criteria for high cut rate and low surface finish values.
U.S. Pat. No. 3,048,482 (Hurst) discloses an abrasive article comprising a backing, a bond system and abrasive granules that are secured to the backing by the bond system. The abrasive granules are a composite of abrasive grains and a binder which is separate from the bond system. The abrasive granules are three dimensional and are roughly pyramidal in shape. To make this abrasive article, the abrasive granules are first made via a molding process. Next, a backing is placed in a mold, followed by the bond system and the abrasive granules. The mold has a pattern of cavities therein which results in the abrasive granules having a specified space-apart pattern on the backing.
Great Britain Patent Application No. 2,094,824 (Moore), published Sep. 22, 1982 pertains to a patterned lapping film. A slurry of abrasive and curable binder resin is prepared and the slurry is applied through a mask to form discrete spaced-apart islands. Next, the resin or binder is cured. The mask can be a silk screen, stencil, wire or a mesh.
U.S. Pat. No. 4,930,266 (Calhoun et al.) teaches a patterned abrasive sheeting in which abrasive granules are strongly bonded and lie substantially in a plane at a predetermined lateral spacing. In this disclosure the abrasive granules are applied via an impingement technique such that each granule is individually applied to the abrasive backing in a spaced relationship. This results in an abrasive sheeting having a precisely controlled spacing of the abrasive granules. An area spacing of 870 granules/square centimeter is described by Calhoun et al.
U.S. Pat. No. 5,107,626 (Mucci) teaches a method of providing a patterned surface on a substrate by abrading with a coated abrasive containing a plurality of precisely shaped abrasive composites. The abrasive composites are in a non-random array and the abrasive composites comprise a plurality of abrasive grains dispersed in a binder.
U.S. Pat. No. 5,219,462 (Bruxvoort et al.) teaches a method for making an abrasive article. A slurry is coated substantially only into recesses of an embossed backing. The abrasive slurry comprises a binder, abrasive grains and an expanding agent. After coating, the binder is cured and the expanding agent activated. This causes the slurry to expand above the surface of the embossed backing to assume a mushroom-like or spherical-like shape. The recesses, when unconnected to necessarily form space-apart composites, are disclosed as typically having an area spacing of 2 to 10,000 recesses/cm.sup.2, preferably 100 to 1,000 recesses/cm.sup.2. Alternatively, the recesses can be connected or linked together to form linearly elongated recesses having a linear spacing of 2 to 100 recesses/cm.
Japanese Patent Application No. S63-235942, published Mar. 23, 1990, teaches a method of a making a lapping film having a discontinuous raised pattern of abrasives. An abrasive slurry is coated into indentations in a tool. A backing is then applied over the tool and slurry containing abrasive grains and curable binder is cured to provide a coated abrasive which is removed from the tool. The binder can be cured by radiation energy or thermal energy to form a networked layer of abrasive material.
Japanese Patent Application No. JP 4-159084 published Jun. 2, 1992 teaches a method of making a lapping tape. An abrasive slurry comprising abrasive grains and an electron beam curable resin is applied to the surface of an intaglio roll or indentation plate. Then, the abrasive slurry is exposed to an electron beam which cures the binder and the resulting lapping tape is removed from the roll to form a networked layer of abrasive material.
European Application 554,668, published Aug. 11, 1993 (Calhoun) teaches a method of making an abrasive article. A slurry of abrasive grains and curable binder is coated into recesses of an embossed substrate used as a molding surface. The recesses are separated from each other and can have a spacing of 2 to 10,000 recesses per square centimeter. The abrasive slurry forms abrasive composites which, upon solidifying of the binder, are entirely separate from each other, and which are then cured with the composites being maintained in a separated state. The embossed surface is then urged against an adhesively-coated backing layer such that the cured abrasive composites are then adhesively bonded to the backing layer. The embossed substrate is separated from the backing and the spaced-apart abrasive composites remain adhered to the backing with no contacting or abutting portions between the composites.
U.S. application Ser. No. 08/120,300 (Hoopman), filed Sep. 13, 1993, relates to an abrasive article where the abrasive composites have precise shapes, but the shapes are not all identical.
U.S. Ser. No. 08/067,708 (Mucci), filed May 26, 1993, pertains to a method of polishing a workpiece using an abrasive article. The abrasive article comprises a plurality of precisely shaped abrasive composites bonded to a backing. During polishing, the abrasive article is oscillated.
However, there remains a need for an abrasive article that can provide a high cut rate while imparting a fine surface finish in a workpiece surface where the arrangement of the abrasive composites does not necessitate a complete physical separation thereof and which encompasses very high densities of abrasive composites.